Electrical thermometer system and sensor therefor

ABSTRACT

An electrical clinical thermometer system including a probe for insertion into a body cavity. A temperature sensor is carried by the probe whose electrical resistance changes with temperature. This probe is connected into a wheatstone bridge circuit which is restored to a balanced condition by an adjustable resistor which is mechanically connected to a readout device that indicates the temperature at the sensor when a meter in the bridge circuit is at its reference setting. The system is insensitive to voltage changes such as from a battery whose voltage declines. The readout device holds its reading when the probe is removed from the cavity, and may be either mechanical or digital. A sensor for this system comprises an elongated metal body with a discontinuity which is bridged by a plurality of fuse-like resistances of different values which can selectively be destroyed so as finely to adjust the resistance of the sensor. Calibration means for the adjustable resistor enable the use of inexpensive, relatively low-tolerance components to secure a very accurate measurement.

United States Patent [1 1 Gould, III

[ Dec. 4, 1973 ELECTRICAL THERMOMETER SYSTEM AND SENSOR THEREFOR [75]Inventor: Edson B. Gould, III, Newport Beach, Calif.

22 Filed: Sept. 30, 1971 21 Appl.No.: 185,280

[52] US. Cl. 73/362 AR, 29/612, 337/31, 337/293, 338/25, 338/28, 338/195[51] Int. Cl. G0lk 7/20, 1101c 3/00 [58] Field of Search 73/362 AR;29/612; 337/293, 297, 31; 338/25, 195, 28; 323/75 H, 75 N [56]References Cited UNITED STATES PATENTS 3,431,781 3/1969 Wiggin 73/362 AR3,478,570 11/1969 Ratnoffm" 73/362 AR X 3,469,449 9/ 1969 Keller 73/362AR 3,494,196 2/1970 Moussette 73/362 AR 3,452,314 6/1969 Sapofi et al...29/612 X 3,339,414 9/1967 Coor 73/362 AR 2,971,379 2/1961 Weisheit....73/362 AR 3,045,488 7/1962 Jurs et al 73/362 AR X FOREIGN PATENTSOR'APPLICATIONS 163,245 6/1964 U.S.S.R 338/195 Primary ExaminerRichardC. Queisser Assistant Examiner-Frederick Shoon Attorney-Angus & Mon

[57] ABSTRACT An electrical clinical thermometer system including aprobe for insertion into a body cavity. A temperature sensor is carriedby the probe whose electrical resistance changes with temperature. Thisprobe is connected into a wheatstone bridge circuit which is restored toa balanced condition by an adjustable resistor which is mechanicallyconnected to a readout device that indicates the temperature at thesensor when a meter in the bridge circuit is at its reference setting.The system is insensitive to voltage changes such as from a batterywhose voltage declines. The readout device holds its reading when theprobe is removed from the cavity, and may be either mechanical ordigital. A sensor for this system comprises an elongated metal body witha discontinuity which is bridged by a plurality of fuse-like resistancesof different values which can selectively be destroyed so as finely toadjust the resistance of the sensor. Calibration means for theadjustable resistor enable the use of inexpensive, relativelylow-tolerance components to secure a very accurate measurement.

12 Claims, 8 Drawing Figures 7 II Ii /I II Ii 0 15.52....

PATENTEDUEC 4 Ian I 3; 776.040 saw 1 or 2 80 H m Iii/'Z/ I I VENTOPATENTEUHEC M975 3,776,040

SHEET 2 BF 2 V II II II II II 015.5%..--

INVENTOR. fDJO/V 5.600111% /i SZM ELECTRICAL THERMOMETER SYSTEM ANDSENSOR THEREFOR I This invention relates to an electrical clinicalthermometer system, and to. a sensor and 'readout device for use withthe same.

Electrical clinical thermometer systems are well known, but all sufferfrom substantial disadvantages. One of the major disadvantages in theprior art resides in the fact that, in general, their readings are takenby means of a meter which indicates the temperature by a needle pointingat a scale while the probe remains in the mouth. In order for such ameter to have sufficient accuracy, it must have jeweled bearings whichcontribute greatly to its expense. Even worse, the rough treatment whichthe device will receive in a hospital soon destroys such a delicateinstrument. Furthermore, the temperature reading must be remembered bythe attendant because it is lost as soon as the probe is removed fromthe mouth. I

To overcome the foregoing objections, there have been provided a numberof means for manually holding the needle at its reading setting, or forproviding holding circuitry for the same purpose. Such features aresubject to malfunction and increase the expense of the device.

Still another objection to the prior art devices resides in the cost ofthe thermistors which are used as sensors. Their expense is such thatthey must be reused, and accordingly, disposable caps are provided toshield the thermistor and to conduct heat to it. This is an inefficienttechnique, and it also requires the insertion of a previously used probeinto a patients mouth.

It is an object of this invention to provide a clinical thermometersystem which can utilize relatively inexpensive circuit components, suchas adjustable resistors and meters, which gives a reading which isobtained manually and retained after the sensor is removed from themouth, the retention of said reading being a consequence of simplyleaving the adjustable element as it was, does not require anyinteraction with the meter or the associated circuitry, and in which thetemperature sensor and probe combination is so inexpensive that it canbe thrown away after each use.

Still another disadvantage of prior art devices resides in theirsensitivity to voltage variations such as can be expected from smallbatteries with limited capacity and life. The system of this inventionperforms accurately regardless of the voltage, and is so insensitive toit that it can even provide a light to illuminate its dial from the samebattery without affecting the accuracy of the reading.

An electrical clinical thermometer system according to this inventionincludes a probe for insertion into a body cavity. A temperature sensoris carried by the probe, and has an electrical resistance which changesas a function of temperature. The sensor is incorporated in a wheatstonebridge circuit, another arm of which includes an adjustable resistorwhich is set by manual means so as to balance a meter in accordance withconventional wheatstone bridge operation. The manual means which setsthe adjustable resistor has a portion such as a shaft whose position isindicative of the reading, and which remains in its adjusted positionafter the probe is removed from the mouth. Readout means (indicia) maybe attached directly to this portion and read mechanically, or a digitalreadout device may be connected to it, as preferred. In both cases the vreading is available even after the sensor is removed from the body.

According to a preferred but optional feature of the invention, thesensor comprises an elongated and ex posed metal layer.

According to still another preferred but optional feature of theinvention, a discontinuity is formed in the sensor which is bridged by aplurality of fuse-like resistances of different values. These canselectively be destroyed in order finely to adjust the resistance of thesensor.

According to another preferred but optional feature of the invention,the adjustable resistance is connected to a first and second calibratingresistance which are provided for setting the maximum and minimum scalereadings, thereby permitting the use of adjustable resistors ofrelatively low precision, and significantly reducing the cost of theunit.

The above and other features of this invention will be fully understoodfrom the following detailed description and the accompanying drawings,in which:

FIG. 1 is a plan view of the presently preferred embodiment of a readoutmember according to the invention;

FIG. 2 is a right-hand side view of FIG. 1, together with additionalportions of the invention;

FIG. 3 is a circuit drawing of the circuitry located within the deviceshown in FIG. 1;

FIG. 4 is an axial cross-section of the presently preferred embodimentof a sensor and probe for use with this invention;

FIG. 5 is a side view of FIG. 4;

FIG. 6 is an'enlarged view of a portion of FIG. 4;

FIG. 7 is a cross-section taken at line 7--7 of FIG. 5; and

FIG. 8 is a section taken at line 88 of FIG. 2.

A readout member 10, according to this invention, is shown FIG. 1. Thismember comprises a case 11 with a handle 12. The case includes anaperture 13 through which a scale 14 and a meter needle 15 are visible.

On the case there is a readout means 16 which comprises a reference mark17 on the case and a rotatable disc 18 which is rotatably mounted to thecase by a shaft 19. Calibration marks 20 in degrees of temperature areprinted around the periphery of the rotatable disc, and the coincidenceof reference mark 17 with one of the calibration marks 20 is the meansfor determining the temperature which has been taken.

The case may conveniently be made of a cover 21 and a base member 22,forming a cavity 23 to receive the elements of circuitry as will laterbe disclosed. The circuitry of FIG. 3 is contained within the cavity 23.Because the circuit components are standard types, they will be shownonly by their electrical symbols.

A socket 24 is provided at the top of the base member to receive prongs25 from a two-wire conductor 26 which extends to a connector 27 to whicha probe 30 is connected. The conductor can readily be connected anddisconnected from the case by removing the prongs from the socket.

A wheatstone bridge circuit is provided which has first, second, thirdand fourth arms 36, 37, 38 and 39, respective- 16, in a hollow squareconfiguration. These arms are connected at first, second, third andfourth terminals 40, 41, 42 and 43, respectively. First resistor 44 isconnected between the first and fourth terminals and 43. Second resistor45 is connected between first and second terminals 40 and 41,respectively. Resistors 44 and 45 have equal values in accordance withknown wheatstone bridge construction. 7

An adjustable resistor 46 is connected to the second and third terminals41 and 42, respectively. The term adjustable resistor is used herein inits generic form to describe any circuit device whose contribution tothe resistance of its respective arm is adjustable. In its most commonform, it has an elongated resistance, such as a winding 47, and anadjustable contact 48 slidable along the winding to determine thatportion of the winding which is included in the circuit. The location ofthe contact along the winding will thereby adjustably determine theresistance in the respective arm. In the simplest embodiment of theinvention, one end of the winding would be connected to one of terminals41 and 42, and the slider to the other. However, a more sophisticatedcircuit is shown for the third arm which enables less expensive circuitcomponents to be used in the construction of this device. For thispurpose, a first adjustable calibration resistor 50, having a winding 51and a contact 52, is connected between the adjustable resistor andterminal 41. A tap 53 connects at a terminal 54 and extends to thecontact 55 of a second adjustable calibration resistor 56, which has awinding 57. This winding is also connected to the contact 48 of theadjustable resistor 46.

The fourth arm 39 incorporates connector means 60 which constitute thesocket 24. The connector means is connected to third and fourthterminals 42 and 43, respectively. It will now be seen that the sensorcan be connected at the connector means 60 into the fourth arm of thewheatstone bridge circuit.

A meter 61 is connected to the second and fourth terminals 41 and 43,respectively. This meter includes needle 15. It is of the type whichbalances at a central portion of the scale in the absence of currentflow through it. Its needle deflects right or left as a consequence ofcurrent flow through the meter. This is a rugged and inexpensive meter,and has only one reading of importance its null position. Readings alongy the scale off-center are unnecessary. The meter case fits in aperture13.

A voltage source 62 such as a battery is connected to first and thirdterminals 40 and 42, respectively. If desired, an off-on switch 63 maybe connected between the battery and one of terminals 40 or 42. In thepreferred embodiment of this invention, a common radio off-on andvolume-control device is utilized. It includes a switch actuated by itsshaft, as well as contact 48, which is moved along the winding byrotation of the shaft. This is schematically shown in FIG. 2. Theclassical construction is that of a cam on the rotatable shaft 19adapted to open and close switch 63, with the contact mounted to theshaft to move along winding 47, which winding is usually arcuate.

A light 63a may be connected in series with the battery and switch so asto be turned on along with the meter, whereby to illuminate the dial.The system is insensitive to voltage variation, and the light does'notupset its accuracy.

Probe 30 comprises an elongated body 64, which is intended to be thrownaway after each use. It carries the sensor 65, which also is intended tobe thrown away after every use, or after the respective patient hasfinished with it after a number of uses.

It is a significant advantage of this invention that the sensor can bemade inexpensively enough that it can be thrown away, thereby to avoidthe problems of contamination. The probe is best shown in FIG. 4. Itsbody 64 has first and second ends 66, 67. At the first end, terminalends 68, 69 of leads 70, 71 are exposed and folded over the end to fitagainst the outside wall of the body. These terminal ends formconductive connections at a socket 72, which forms part of connector 27.

FIG. 8 shows the open end of the socket with a cavity 73. It has agenerally ovular section, which also is the general shape of the probe.This arrangement aligns the connecting elements at this connector. Apair of exposed arcuate plates 74, 75 in this cavity are borne againstby the terminal ends 68 and 69 so as to make conductive contact atconnector 27. The ends of the leads are preferably so fragile that,while they can readily be shoved into the socket, upon removal they areapt to be frayed and torn, thereby rendering the probe unsuitable for asecond usage. Should the probe be intended for more than one usage, thenthese terminal ends will bemade sufficiently strong that they will notbe destroyed by the removal process, or will simply be kept assembledwith the same conductor 26.

Sensor is placed in an opening at the second end 67 of the probe. It isexposed to fluids in the body cavity.

The sensor may readily be manufactured by thin film depositiontechniques, thick film" screening techniques, or by circuit-boardtechniques, as preferred. The sensor includes a base member 77, uponwhich is deposited, or otherwise applied, and an elongated metal member78, preferably in the form of a deposited layer. The member terminatesat a pair of terminal patches 79, 80, to which leads 70 and 71 areconductively attached. Even though gold is the preferred material ofconstruction for the thermally sensitive portion of the sensor, solittle of it is required that the device remains commercially practicaland low in cost. A gold layer approximately 200 angstroms thick is thepreferred material for member 78.

In order to provide for sufiicient resistance in the small area, thelayer is preferably made serpentine in shape, and has a discontinuity 81which is bridged by a plurality of fuse-like resistance elements 82, 83,84, 85, 86, whose widths differ from one another by various increments.It is possible to standardize the resistance of the sensor so as toproduce sensors of great accuracy with mass production techniques byapplying current pulses of such value as to blow these fuselikeresistance elements in whatever combination is required to leave behindonly those bridges which will result in a sensor of the desiredresistance at a given temperature. Accordingly, a fine tuning of theresistance is possible simply by heating the sensor to a desiredstandard temperature, and then, by applying pulses of appropriatemagnitude, blowing such of these fuses as is necessary in order to givethe layer the necessary resistance at the given temperature. This is aninexpensive and rapid procedure, and results in a very inexpensive andhighly accurate sensor.

The surface of the metal member 78 is readily sterilized, and will notbe adversely affected by body fluids. The layer is tough and resistantto the abrasion it is likely to encounter. If desired, however, aprotective coating may be applied over the layer, although this will notordinarily be necessary. Further, if desired, the

sensor may be somewhat recessed in the opening in order to give ameasure, of mechanical protection to member 78. i

Gold is the preferred metal for making member 78 because of itsfavorable relationship between temperature and resistance, especially inthin films. Other materials exhibiting similar resistance-temperatureproperties, both metallic and non-metallic, may be used instead.Preferably, one will be selected which is readily applied. Standardthermistors may also be used, sacrificing, however, the economicbenefits of the sensor described above.

To calibrate the readout member, a standard resistor having theresistance of the sensor at its highest measurement temperature, say106, isconnected to connector 60. Adjustable resistor 54 is set towardits zero resistance with the indicia for 106 adjacent to reference mark'17. First calibration resistor 50 is adjusted so as to return the meterto null. The upper scale limit is now established.

Next, a standard resistor having the resistance of the sensor at itslowest measurement temperature, say 94, is connected to connector 60.Adjustable resistor is set toward its maximum resistance, with theindicia for 94 adjacent to reference mark 17, and second calibrationresistor 56 is adjusted so as to return the meter to null. The lowerscale limit is now established.

Note particularly that the readout member is now closely calibrated tothe ends of its scale, and an adjustable resistor, having relativelybroad tolerances, such as about l-2 percent deviation from linearity,can be used. This constitutes a very important savings, because the twocalibration resistors can also be made to wide tolerances. There resultsa device with very high accuracy made from commercial parts oftransistorradio quality.

The device is now ready to be used, and further calibration of resistors50 and 56 will not be required. Accordingly, their means for adjustmentwill be enclosed within the case so that they cannot be tampered with.The means for setting the adjustable resistor 46 is connected to shaft19 which projects through the case. To use the system, the probe isinserted into socket 72, and conductor 26 is joined into the circuit atsocket 24. Then, when the probe is inserted into the body cavity, if theresistance of resistor 46 is not already set exactly where it should beto balance out the meter, the disc is turned until the meter is restoredto its balanced position, adjusting the resistance of adjustableresistor 46 in so doing. When the needle is set at its balanced point,such as zero" in FIG. 1, it is known that the temperature has beenmeasured. The probe may then be removed from the cavity. The temperaturereading is retained because there is no further need to turn therotatable disc. It simply remains set, and the reading can be copied bythe attendant at a later time or at a place removed from the patient.

The rotational position of shaft 19 is the source of the readout data.It is evident that the simplest readout means is that shown a dial onthe shaft. However, there may instead be provided many equivalents whichfall within the scope of the invention. For example, rotary to axialindicators such as a spur gear on the shaft driving a slide along ascale. Such is an example of a mechanical equivalent.

FIG. 2 also shows an electronic equivalent, wherein an electronicdigital readout device 80 is controlled by shaft 19. In such a device,shaft 19 would drive a potentiometer (not shown), whose output isconverted by the digital readout to a legible numerical array inaccordance with known principles that form no part of this invention. Itdoes indicate the wide range of read-out means available to this system.

This device can utilize an extremely rugged and tough meter, because itis not necessary for it to be read to graduations extending over anentire scale. Instead, it is only necessary for this meter to be read ata single null condition. Accordingly, rugged meters, which do not haveto use jeweled bearings, can be utilized, and the cost of the device isgreatly reduced.

This invention thereby provides an inexpensive readout device and aninexpensive probe, both of which can readily be produced to hightolerances from inexpensive components and with economical manufacturingtechniques, thereby to provide a readout means which does not requirethe use of memory by the attendant or complicated means for holdingmeter readings or circuit settings.

Because the system is a balanced one, the voltage across terminals and42 is immaterial to the measurement of the temperature. Therefore thecondition of the battery is unimportant to the accuracy of theinstrument, which constitutes an important advance in this art.

This invention is not to be limited by the embodiments shown in thedrawings and described in the description, which are given by way ofexample and not of limitation, but only in accordance with the scope ofthe appended claims.

I claim:

An electrical clinical thermometer system comprising: a probe forinsertion into a body cavity; a temperature sensor carried by the probeand having an electrical resistance which changes as a function oftemperature, said sensor comprising an elongated metal layer, therebeing a discontinuity in the said layer which is initially bridged by aplurality of fuse-like resistances of different resistance values,whereby an adjustment of the resistance value of the sensor can be madeby destroying the continuity of selected ones of said fuse-likeresistances, there remaining in place and bridging the discontinuity atleast one of said fuse-like resistances; a wheatstone bridge circuithaving four arms joined in a hollow square at four terminals; a firstand a second resistor connected in a first and a second one of saidarms, connected to each other at the first of said terminals, said firstand second resistors being of equal value; an adjustable resistor in athird of said arms connected at the second of said terminals with saidsecond resistor, and also connected to the third of said terminals;connector means connected to said ad justable resistor at said thirdterminal and to the first of said resistors at the fourth of saidterminals, said connector means being adapted to connect said sensorinto the fourth arm; a voltage source connected to the first and thirdterminals; a meter connected to said second and fourth terminals; andreadout means calibrated in degrees of temperature whose reading isdetermined by the value of the resistance required in the third arm inorder to balance that of the sensor, and thereby to set the meter to abalanced setting.

2. A thermometer system according to claim 1 in which the sensorcomprises an elongated and exposed metal layer.

3. A thermometer system according to claim 2 in which the metal of thelayer is gold.

4. A thermometer system according to claim 1 in which a switch isconnected between the voltage source and one of the first and thirdterminals.

5. A thermometer system according to claim 1 in which the third of saidarms further includes a first and a second calibration resistor forsetting the resistances in said third arm respective to sensorresistances respective to maximum and mimimum temperatures to bemeasured.

6. A thermometer system according to claim 5 in which the firstcalibration resistor is serially connected to the adjustable resistorand to the second terminal, the second calibration resistor is connectedto the first calibration resistor and to the adjustable resistor attheir mutual connection, and to an adjustable portion of said adjustableresistor.

7. A thermometer system according to claim 1 in which the resistance ofthe adjustable resistor is set by manual means, and in which the readoutmeans comprises visual calibration carried by said manual means.

8. A thermometer system according to claim 7 in which the said manualmeans is a rotatable member mounted to a rotatable shaft which sets theadjustable resistor.

9. A system according to claim 1 in which said means calibrated indegrees of temperature is a digital readout.

10. A thermometer system according to claim 1 in which a lamp isconnected in circuitry between the first and third terminals.

11. A sensor for an electrical thermometer comprising: a base, and anelongated layer of metal on and adherent to said base, said metal havingthe property of changing resistance with temperature, there being adiscontinuity in the said layer which is initially bridged by aplurality of fuse-like resistances of different resistance values,whereby an adjustment of the resistance value of the sensor can be madeby destroying the continuity of selected ones of said fuse-likeresistances, there remaining in place and bridging the discontinuity atleast one of said fuse-like resistances.

12. A sensor according to claim 11 in which the metal of the layer isgold.

1. An electrical clinical thermometer system comprising: a probe forinsertion into a body cavity; a temperature sensor carried by the probeand having an electrical resistance which changes as a function oftemperature, said sensor comprising an elongated metal layer, therebeing a discontinuity in the said layer which is initially bridged by aplurality of fuse-like resistances of different resistance values,whereby an adjustment of the resistance value of the sensor can be madeby destroying the continuity of selected ones of said fuse-likeresistances, there remaining in place and bridging the discontinuity atleast one of said fuse-like resistances; a wheatstone bridge circuithaving four arms joined in a hollow square at four terminals; a firstand a second resistor connected in a first and a second one of saidarms, connected to each other at the first of said terminals, said firstand second resistors being of equal value; an adjustable resistor in athird of said arms connected at the second of said terminals with saidsecond resistor, and also connected to the third of said terminals;connector means connected to said adjustable resistor at said thirdterminal and to the first of said resistors at the fourth of saidterminals, said connector means being adapted to connect said sensorinto the fourth arm; a voltage source connected to the first and thirdterminals; a meter connected to said second and fourth terminals; andreadout means calibrated in degrees of temperature whose reading isdetermined by the value of the resistance required in the third arm inorder to balance that of the sensor, and thereby to set the meter to abalanced setting.
 2. A thermometer system according to claim 1 in whichthe sensor comprises an elongated and exposed metal layer.
 3. Athermometer system according to claim 2 in which the metal of the layeris gold.
 4. A thermometer system according to claim 1 in which a switchis connected between the voltage source and one of the first and thirdterminals.
 5. A thermometer system according to claim 1 in which thethird of said arms further includes a first and a second calibrationresistor for setting the resistances in said third arm respective tosensor resistances respective to maximum and mimimum temperatures to bemeasured.
 6. A thermometer system according to claim 5 in which thefirst calibration resistor is serially connected to the adjustableresistor and to the second terminal, the second calibration resistor isconnected to the first calibration resistor and to the adjustableresistor at their mutual connection, and to an adjustable portion ofsaid adjustable resistor.
 7. A thermometer system according to claim 1in which the resistance of the adjustable resistor is set by manualmeans, and in which the readout means comprises visual calibrationcarried by said manual means.
 8. A thermometer system according to claim7 in which the said manual means is a rotatable member mounted to arotatable shaft which sets the adjustable resistor.
 9. A systemaccording to claim 1 in which said means calibrated in degrees oftemperature is a digital readout.
 10. A thermometer system accorDing toclaim 1 in which a lamp is connected in circuitry between the first andthird terminals.
 11. A sensor for an electrical thermometer comprising:a base, and an elongated layer of metal on and adherent to said base,said metal having the property of changing resistance with temperature,there being a discontinuity in the said layer which is initially bridgedby a plurality of fuse-like resistances of different resistance values,whereby an adjustment of the resistance value of the sensor can be madeby destroying the continuity of selected ones of said fuse-likeresistances, there remaining in place and bridging the discontinuity atleast one of said fuse-like resistances.
 12. A sensor according to claim11 in which the metal of the layer is gold.